The search for environmentally responsible disposal techniques of waste products is an issue that has been a problem in the past, and will continue to be a significant problem for the future. The United States Environmental Protection Agency in its February 1989 "Agenda For Action" estimated the annual generation of municipal solid waste will increase from 160 million tons (1988) to 193 million tons by the year 2000. While the quantity of refuse generated increases, capacity for waste containment decreases. The problem is heightened in regions of high population density, such as major metropolitan centers, where the landfill sites being used for disposal of municipal solid waste are at or near maximum capacity, and the mere suggestion of building a new landfill site incenses neighboring communities. Moreover, the continued use of even existing landfill sites raise a myriad of issues. For example, landfill sites are often unsuitable for development for many years, in part due to the natural subsidence of the refuse within the landfill. Landfill sites are also potential sources of both water and air pollution, which thus mandates segregation of the landfill from populated environs. Yet, landfill capacity is vital-in that currently over 90% of the refuse generated is housed within the landfill system. Therein lies the problem.
One solution involves increasing the rate of degradation within the currently existing landfill sites such that these landfills can either be reused or transformed into productive land. The use of currently existing landfill sites does, however, necessitate finding a method to secure these landfills so that their mere presence no longer constitutes an environmental menace.
Presently, the rate of landfill degradation is at the mercy of mother nature. Depending on a multitude of variables, such as temperature, pH and moisture content, the rate of degradation within the landfill could vary significantly. What is required to achieve degradation is a balance of many variables, together with sufficient moisture and nutrient content. In a municipal landfill, such requirements are rarely met. As a result, landfills generally undergo stabilization at a very slow rate and at certain periods the mix of variables results in zero degradation.
During the stabilization process a municipal solid waste landfill will go through several identifiable phases.
The first phase is named the initial adjustment period and occurs during waste placement and moisture accumulation.
The second phase (transition) is identified when leachate is generated and the landfill converts from aerobic into anaerobic microbial activity. At this time volatile organic acids appear in the leachate in increasing concentrations.
During the third (acid formation) phase, intermediary volatile organic acids are dominant and pH decreases. Nitrogen and phosphorus support the microbial biomass and hydrogen gas may be detected. The low pH may increase metal mobilization.
The fourth phase (methane fermentation) occurs as the intermediary volatile acids are converted into methane and carbon dioxide. The organic strength of the leachate is reduced as gas production increases. The pH returns to a neutral level and complexation and precipitation of metal occurs.
In the final phase, or maturation, nutrients may become limiting as microbial stabilization of organic constituents is completed. The landfill is more stable, and humic-like (soil-like) substances may be produced. Metals may become mobilized if they complex with constituents in the humic-like substance. Unfortunately, decades and sometimes generations are required for this natural stabilization process to completely decompose the waste. All the while, these landfills are incapable of housing additional waste or becoming otherwise productive land.
This and other concerns become particularly daunting when one examines the specific problems associated with unsecured landfills. Prior to the introduction of modern sanitary landfills, "landfills" constituted a dumping pit with no control measures or implementations for curbing the environmental dangers associated therewith. Presently there are at least 2,000 to 3,000 of these "unsecured landfill" sites within the United States. The term "unsecured landfill" constitutes those landfills which have no protective lining to separate the landfill area from the surrounding environment. In contrast, a secured landfill has protective barriers surrounding the landfilled material. Hence, a secured landfill has a protective bottom liner to act as a barrier from the soil and/or a means for capping the entire landfill from air or other environmental contamination. Devoid of such a protective barrier, an unsecured landfill poses a substantial threat to its surrounding environment.
In particular, the landfill refuse and its by-products may contaminate the surrounding ground water via action of the natural movement of water through the ground. Thus if the refuse within the landfill is not somehow treated or isolated, the refuse can spread beyond the original landfill area through the ground water system, endangering water supplies. In order to avoid these results, there exists a need to treat and "secure" these unsecured landfill sites.
To comprehend different treatment techniques an analysis must be made of the composition of a particular landfill. Landfills generally contain a wide variety of refuse including organic material, some of which undergo anaerobic decomposition. During degradation and further when a liquid such as rain water or ground water comes in contact with the refuse, leachate is formed. During degradation, by a process of liquefaction, a landfill produces leachate. Leachate generally contains high concentrations of various contaminants including ammonia, nitrogen compounds, chemical oxygen demand, volatile organic compounds and possibly heavy metals. As a result, state and federal landfill regulations now contain stringent standards for collecting and treating leachate. The previous focus has therefore been placed on removing leachate from landfills. One such process is shown in U.S. Pat. No. 5,238,580 issued Aug. 24, 1993, A Method For Treating Leachate From a Sanitary Landfill. The method disclosed includes the steps of adding a pH adjuster to elevate the pH of the leachate, such that ammonia nitrogen compounds, COD compounds and volatile organic compounds can be stripped from the leachate; heavy metals form insoluble compounds; combusting landfill gas to produce combustion products and to elevate the temperature of the leachate such that chemical activities enhance therein; precipitating the insoluble compounds from the leachate; and diffusing the combustion gases through the leachate to reduce the pH thereof to any acceptable discharge level. Therefore, in order to prevent problems associated with the existence of leachate, volatile contaminants are removed from the leachate by gas stripping. The landfill gas, subsequent to passage through the gas scrubber, is then directed to a combustion device. A disadvantage of this process is that the process disclosed requires a complex and expensive treatment procedure. Moreover, the process is very slow because the leachate collected and then subsequently treated is limited by the ambient conditions of the landfill. The soil structure and the natural rate of movement of water through the soil can retard creation of leachate and thus tremendously increase the amount of time required to effectively remove the leachate from the landfill. Lastly, gas stripping releases pollutants to the atmosphere and the pollutant is merely being moved from the water we drink to the air we breathe.
In situ remediation of landfills is generally known in the art. One approach to rendering in situ remediation is suggested by U.S. Pat. No. 4,396,402 which teaches a process for improved gas production providing higher gas production rates and yields by accelerated bioleaching of organic wastes. Two phase digestion is used under controlled digester conditions in the process of this invention, that is acid phase digestion is used to promote the growth of the acid forming bacteria and a second methane phase digestion is used to promote the growth of the methane producing organisms. The leachate is thus passed through the digestion phases and then subsequently recycled through the landfill and then back to the digesters. The problem associated with this invention, includes the need for two digesters to promote the formation of both acid forming microorganisms and methane forming microorganisms. Second, the disclosed remediation technology offers no solution for the particular problems associated with unsecured landfills, specifically the need for groundwater control.
Each of the above-mentioned patents suffer from a failure to provide an economic and efficient system for the confinement and remediation of unsecured landfills.